The technology of coplanar lines (CPWS, coplanar waveguides) is used for high-frequency circuits, particularly in the millimeter wave range, since coplanar lines demonstrate superb high-frequency properties, especially in connection with microelectromechanical switches for high-frequency signals.
The construction of a coplanar line, as it is known from the related art, is shown in FIGS. 1a and 1b, FIG. 1a showing a section through a structural element having a coplanar line and FIG. 1b showing a top view onto the surface of the structural element. The structural element is constructed from a substrate 1, which may be made up of a plurality of layers. On uppermost substrate layer 2 there are situated a neutral wire 3 of width w and thickness tW and two outer conductors 4 and 5 having widths ba and bb and thicknesses ta and tb. The two outer conductors 4 and 5 here run parallel to neutral wire 3. The gaps between neutral wire 3 and outer conductors 4 and 5 have the same width ga and gb, which does not have to be that way for every coplanar line. Neutral wire 3 is used as a signal conductor. The line geometry for a certain impedance at a certain frequency is a function of the material parameters and thicknesses of the substrate layers and the conducting layer in which neutral wire 3 and outer conductors 4 and 5 are implemented. This structure may be covered by one or a plurality of overlayers.
A line termination for a coplanar line which is implemented, for example, on calibration substrates for network analyzers, is shown in FIG. 2. In this application, the line dimensions are relatively small. 50 μm neutral wires are typical. The line termination includes, in this case, two resistor elements 6 which are positioned orthogonally to the direction of the coplanar line, i.e. orthogonally to neutral wire 3 and to outer conductors 4 and 5. The resistor elements are trimmed to a direct current resistance of exactly 50 Ohm (+/−0.3%). Thereby, in the range of 50 . . . 110 GHz, matching of ca 30 . . . −25 dB is achieved. Under ca 26 GHz the matching is better than −35 dB.